Encapsulation has proved to be an especially favored method for the disposal of certain waste materials; specifically it provides a suitable means for the conversion of these materials into a stable and safe form, which allows for long-term storage and/or ultimate disposal. The technique can find particular application in the nuclear industry, where the highly toxic nature of the materials involved, and the extended timescales over which the toxicity is maintained, are the principal considerations when devising safe disposal methods.
Whilst the technique of encapsulation can be of great value in such circumstances, however, it is known from the prior art that many fine particulate sized waste materials, as well as certain filters which contain ion exchange resins, are particularly problematic to encapsulate. This is a problem which becomes especially important in the nuclear industry where, in view of the nature of the waste products, it is vital to ensure that procedures are completed efficiently and successfully before disposal of the waste products.
Previously, it has been found necessary to treat these problematic materials by removing them from the containers in which they are stored and mixing them in drums with the encapsulation material, or subjecting them to vibro-grouting techniques. Such procedures, involving removal from containers, are invariably difficult, messy and expensive to carry out, and generally give rise to copious amounts of additional waste. Furthermore, there are obvious implications in terms of extra containment requirements and additional plant capacity.
In general, therefore, the situation is unsatisfactory. Indeed, no commercially acceptable means of dealing with such waste materials is yet available which does not rely on the technique of in-drum mixing which, as previously discussed, has several serious practical drawbacks.
The use of cement based injection grouting in the construction industry is well known from the prior art. Thus, EP-A-412913 teaches the use of a Portland Cement based grout in the consolidation of concrete structures affected by fine cracks, providing a cost-effective means of in filling both superficial and deeper fissures and cavities in such structures, including such as buildings, bridges and dams. Similarly, ZA-A-9209810 is concerned with a pumpable, spreadable grouting composition incorporating a cementitious and/or pozzolanic or equivalent material, and its application in sealing fissures and cracks, back-filling, providing mass fills in civil and mining works, or lining tunnels.
Also disclosed in the prior art are hydraulic setting compositions comprising particles of Portland Cement together with fine particles of silica fume containing amorphous silica, which are the subject of EP-A-534385 and are used in the production of concrete, mortar or grout having improved fluidity, whilst GB-A-2187727 describes a rapid gelling, hydraulic cement composition which comprises an acrylic gelling agent, a fine filler and Portland Cement, this composition being thixotropic and finding particular application in the formation of bulk infills for underground mining, and in the filling of voids and cavities in construction or civil engineering. A composition which also is useful in general building and construction work, and as an insulating material comprises a particulate filler, cellulose fibres and a cementitious binder, and is disclosed in GB-A-2117753.
Whilst the majority of these compositions of the prior art have a requirement for the addition of water, EP-A-801124 is concerned with a dry mixture, used for fine soil injection grout preparation, the mixture comprising fillers which do not react with water, cement and deflocculant; on addition of water, an agglomerate-free fine grout is formed, and this is easily injected into fine soil.
Thus, the use of such grouting materials in—primarily—civil engineering is well known. Surprisingly, the present inventors have now found that it is possible to make use of these materials in order to overcome many of the problems associated with encapsulation of fine particulate sized wastes which have previously been detailed. Thus, it is now possible to provide a treatment method for wastes of this type which affords much greater efficiency, convenience and safety in handling, and has a consequent beneficial effect both in terms of environmental considerations and cost.